Combining Power Souces

[Mike Whiskey]

I have a 100kw solar system being fitted to power a pump through the summer but will be idle 9 months of the year so would like it to power the house during that time, problem being it is 800meters(415v) away so the cost of cable limits the amount power to 20-25kw to be viable.
Is there any way this could be backed up from the the houses own supply other than having separate circuits.

Thanks Mike.

 

[champagnecharly]

I'm not an electrician or installer.. but thoughts are:
Firstly that's one hell of a home generation. What kind of pump is that for?
What is your actual estimated output in those other 9 months of the year. Have the estimations been calculated?

1) If you have a higher DC voltage outage. you will reduce voltage drop and therefore the necesery cable SA will reduce. locating the inverter in a positon that would suit both uses. .
2) Would Multiple cables be more economical?
3) What is your home's power consumption. How much power do you actually use?

 

[Mike Whiskey]

70kw irrigation pump. On second thoughts it would probably be cheaper to buy a second system for the farm rather than buy a big enough cable.

 

[champagnecharly]

70kw irrigation pump. On second thoughts it would probably be cheaper to buy a second system for the farm rather than buy a big enough cable.

The question would be to enough to carry what? How much do you actually need at the house. Running at 600v and 30amp 18kw you can run through 35mm cable. 2 core swa 8.50/m about 5.3% loss on 32mm/awg2 cable. So I believe that's within max loss. At 1600 Should be less than a whole system if you can get arrays arranged to output 600v.

 

[kerching]

600V, 32mm cable....I'm confused; in my defence I have not been paying attention

 

[binky]

I have a 100kw solar system being fitted to power a pump through the summer but will be idle 9 months of the year so would like it to power the house during that time, problem being it is 800meters(415v) away so the cost of cable limits the amount power to 20-25kw to be viable.
Is there any way this could be backed up from the the houses own supply other than having separate circuits.

Thanks Mike.

If your house is single phase, then linking to a 3 phase system is a can of worms...

Rough thoughts on this would be to disconnect house supply from the grid and run everything from the water pump supply.

 

[binky]

Quick internet search on 32mm SWA cable, 3 core, at £21 a meter means 800m of that would cost around £16,800. Ouch!

So suggestion for you, install high speed 3 phase EV charging and sell leccy to local ev owners. Perhaps add a farm shop whilst you are at it, or one of those self service milk machines or something similar.

 

[champagnecharly]

Quick internet search on 32mm SWA cable, 3 core, at £21 a meter means 800m of that would cost around £16,800. Ouch!

Could you not use 2core SWA here is cheaper £8/m. Why not run it at higher voltage DC?
It must be forgotten that running kind of energy back into the grid would over time pay off some of the initial investment.

Excelent idea re selling the service to the end user.

 

[binky]

Could you not use 2core SWA here is cheaper £8/m. Why not run it at higher voltage DC?
It must be forgotten that running kind of energy back into the grid would over time pay off some of the initial investment.

Excelent idea re selling the service to the end user.

If it's £8 it isn't 32mm

You could run DC, but that means locating the inverters 800m from the array, that would seriously affect inverter efficiency.

The other obvious choice is to get a payment for exported leccy to the grid. I am assuming there will be a grid connection at the pump end. Someone like Octopus may be worth talking to, or one of the other green energy suppliers. 100kw is big enough to interest those sorts of companies.

 

[champagnecharly]

If it's £8 it isn't 32mm

2 core SWA 35mm2 is what it says. check the link i had posted. and which is again here: Link. maybe I'm mistaken

You could run DC, but that means locating the inverters 800m from the array, that would seriously affect inverter efficiency.

No doubt my lack of knowledge here has left me confused... How would the inverter efficiency change? Would any additional loss not be from the cable resistance./ voltage drop? And the efficiency of the inverter be the same?
.

 

[champagnecharly]

The other obvious choice is to get a payment for exported leccy to the grid. I am assuming there will be a grid connection at the pump end. Someone like Octopus may be worth talking to, or one of the other green energy suppliers. 100kw is big enough to interest those sorts of companies.

But that would be the best especially if the daily usage on the farm can be offset against the energy production.

 

[binky]

2 core SWA 35mm2 is what it says. check the link i had posted. and which is again here: Link. maybe I'm mistaken


No doubt my lack of knowledge here has left me confused... How would the inverter efficiency change? Would any additional loss not be from the cable resistance./ voltage drop? And the efficiency of the inverter be the same?
.

Bargain, i didn't look properly the first time, but that's still over £6k.

Not my best explanation, so, 100kw array, will be at a rough guess at least 20 DC cables to run 800m that's a shed load of cabling between array and inverter, and assuming buried in ducting, also means problems with heating from cable bunching. I'm not sure what size cable you would need over that distance, but undersize it at all and that will slightly strangle the DC input to the inverters, which on dark winter days, and start-up/ shutdown times of day will drop the inverter power to its lower efficiency operation for longer periods of time. If you look at any solar farm, they have multiple substations to keep the DC runs as short as possible, usually about 200m max. You are far better off keeping the inverters close to the array and running AC back to the house, which can be done with a single cable.

 

[champagnecharly]

Bargain, i didn't look properly the first time, but that's still over £6k.

Not my best explanation, so, 100kw array, will be at a rough guess at least 20 DC cables to run 800m that's a shed load of cabling between array and inverter, and assuming buried in ducting, also means problems with heating from cable bunching. I'm not sure what size cable you would need over that distance, but undersize it at all and that will slightly strangle the DC input to the inverters, which on dark winter days, and start-up/ shutdown times of day will drop the inverter power to its lower efficiency operation for longer periods of time. If you look at any solar farm, they have multiple substations to keep the DC runs as short as possible, usually about 200m max. You are far better off keeping the inverters close to the array and running AC back to the house, which can be done with a single cable.

The other person had mentioned limiting to 24Kw so 1 cable at 600V would.. but yes i didn't dark days into account.

But running AC back to the house at 415 would require massive cables. and assuming its 3 phase additional cores. Huge expense.

Can old 6.6KV transformers be used/recommissioned to run overhead?

Of course feeding into the grid would be the cheapest simplest especially if the suplier/customer will offset the farm usage.

 

[binky]

The other person had mentioned limiting to 24Kw so 1 cable at 600V would.. but yes i didn't dark days into account.

But running AC back to the house at 415 would require massive cables. and assuming its 3 phase additional cores. Huge expense.

Can old 6.6KV transformers be used/recommissioned to run overhead?

Of course feeding into the grid would be the cheapest simplest especially if the suplier/customer will offset the farm usage.

Inverters don't take a single feed, they are designed with multiple MPPTs requiring multiple inputs. So plan A is a non starter.

3 phase back to a house probably wired for single phase, another issue, but 3 phase would use smaller cables oddly enough.

Could use transformers, but that's something I've never looked at. How much are they? I'm guessing £6k or more.

It's almost certainly just cheaper and easier to supply the house with it's own array.

 

[champagnecharly]

Inverters don't take a single feed, they are designed with multiple MPPTs requiring multiple inputs. So plan A is a non starter.

Ok. I bow your expertise.. . I was under the impression it was possible but then there is the current limitation. .

3 phase back to a house probably wired for single phase, another issue, but 3 phase would use smaller cables oddly enough.

Its a farm not house so maybe it is 3 phase...
Can 3 phases be split to 3 Consumer units without an inverter?

Could use transformers, but that's something I've never looked at. How much are they? I'm guessing £6k or more.

Plus cost of poles etc. Couple on ebay 1100KVA @ £4.7K and 800KVA £2.7K but that's cheaper than cables. @ 6.6KV Certainly not a DIY though..

It's almost certainly just cheaper and easier to supply the house with it's own array.

Would the investment in the infrastructure. ie transformer working at a fraction of it's rating outlast the cost in panels and dedicated inverter etc. ?

Seems such a shame not to utilise that kind of what essentially would be free wasted power. assuming usual house usage its enough for heatpump, car charging and normal consumption.. neighbour's cars too.

 

[binky]

Linking 3 phase to 3 phase is far more achievable, you will need to assess the farm for demand and work from that. I'm trying to think how the DNO would respond to linking 2 grid supplies ( probably won't be happy) but, as I said in an earlier post, it may be viable to disconnect the farm from the grid and supply via the pump grid supply/ solar.

I would seriously explore 'green energy suppliers ' and their willingness to buy surplus energy from the solar array. If you can get a decent offer, then it may pay for the farm's energy use.